Various implantable drug delivery devices are known in the art which can be programmed to deliver a drug to a body site for infusion at flow rates and times dictated by a stored drug delivery profile. Such delivery devices typically include a refillable reservoir for storing a fluid drug and a controllable fluid transfer device (e.g., a pump or valve) for transferring fluid from the reservoir to a catheter for delivery to the body site. The drug delivery profile comprises a data set specifying a schedule of flow rates for a periodic cycle, or period, of a certain duration. For example, the duration of a period can be one day, one week, or one month, etc. The particular profile used to control drug delivery is typically specified by the patient's clinician and depends upon several factors including the particular drug formulation being delivered, the patients condition, the therapy being administered, etc.
Most modern drug delivery devices permit a clinician to modify a patient's drug therapy by modifying a stored delivery profile, and/or replacing the current, or old, drug with a new drug. As used herein, the term “new” drug refers to a change in formulation and is intended to include a change in concentration and/or a change in active components. Regardless, if an old drug is replaced by a new drug, then a Current Profile must also be changed to assure that the new drug is properly delivered with regard to safety and efficacy.
Modern implantable drug delivery devices generally permit a clinician to evacuate the volume of old drug from the reservoir prior to introducing a new drug. Although the reservoir can be evacuated, a certain amount of old drug generally remains in the system, typically in the pump (i.e., pump clearance space) and catheter (i.e., catheter clearance space). Any old drug remaining in the system is typically cleared by delivery to the patient's body site. Although, it is generally desired to clear the old drug rapidly in order to promptly initiate the new therapy, the delivery rate must not be so rapid as to jeopardize the patient's health or safety. In any event, the delivery profile for the old drug is generally different than the profile for the new drug. Traditionally, the transition from an old drug to a new drug is typically handled by the clinician calculating a “bridge bolus” to rapidly clear the old drug. Calculation of this bridge bolus and the associated bolus rate is generally time consuming for the clinician and represents an opportunity for human error.